Polycarbonate film comprising an aromatic polycarbonate resin is used as an electrode substrate and a phase difference sheet of a liquid crystal display apparatus due to its high thermal resistance, transparency and optical elastic modulus and so forth. Especially, aromatic polycarbonate film produced by a casting method is preferably used.
In the production of a film poor in lubricity like an aromatic polycarbonate film having a smooth surface, there have been large practical problems during its production. For example, scratches are generated and fine surface-abrasions are formed while the film runs on a transferring roll system. Its poor taking-up property will cause wrinkles to form on the film during the taking-up process, and abrasions to form due to the friction between films when wound too strongly. Therefore, following countermeasures are currently taken for the film having poor lubricity: a lubricant is compounded in the film (for example, Japanese Unexamined Patent Publication No. 8-334607); a surface protecting film having excellent lubricity is laminated on the film; or the film is wound-up with a spacer between films; and so forth. However, when the lubricant is compounded, the formed film will have a critical problem in optical use because of its lowered transparency. On the other hand, the method that uses the surface-protecting film-spacer is accompanied by a production problem, that is, the production process becomes complicated, and the number of the members which are necessary for production is increased.
In order to solve these problems, for example, Japanese Unexamined Patent Publication No. 8-175808 discloses a process for winding up a lubricant-free film which is characterized in that concavo-convex forms are formed on at least one side of the surfaces at both the edges of the film in such a state that the height of the protruding parts is higher than the average height of the film, and subsequently the film is taken up into a roll shape with a winder. In this method, concavo-convex forms are formed on both the edges of a stretched film formed by a melt extrusion method by pushing a rough-surface processing roll which has been internally heated onto the film. However, the film formed by this method is not preferred for optical use because it has defects characteristic of melt extrusion, that is, foreign materials such as heat degradation products or carbonized products. Further, this method has not only a problem of increased energy cost due to the positive heating of the rough-surface processing roll, but also it has such a problem that when the taken-up film having concavo-convex forms at both the edges is taken out from the roll for processing, the surface of the film sometimes unevenly comes into contact with the surface of the transferring roll, and thereby it is sometimes necessary that both the edges having the concavo-convex forms are cut off before processing. Furthermore, both the edges having the concavo-convex forms can not be used as a film of normal quality, and as a result, the waste parts become large.
Thus, the conventional technologies such as the method to achieve the object by improving lubricity of the film by compounding it with a lubricant, or the method in which the film is taken up after concavo-convex forms have been imparted to the edges of the film, still have problems unsolved.